The present invention relates to an ink-jet printer which prints an image onto a print medium held on a rotary drum with ink ejected from a print head, and more particularly, to an ink-jet printer whose print head is constituted by a plurality of ink-jet nozzles disposed in the axial direction of the rotary drum.
The popularity of serial-type ink-jet printers is spreading. In the serial-type ink-jet printer, a print head and an ink cassette of a relatively small capacity are integrally mounted on a carriage, and the carriage is movably attached to a guide bar extending across a paper sheet. The paper sheet is fed in a direction perpendicular to the guide bar at a constant pitch, and the carriage is moved along the-guide bar each time the paper sheet is fed for one pitch. The print head ejects ink during the movement of the carriage. In the case where the printer is used for color printing, the print head includes a plurality of ink-jet nozzles which are respectively supplied with inks of different colors from ink tanks. In the structure as described above, for example, a color image of A4 size is printed out in about ten minutes. Thus, the serial-type ink-jet printer operates at a slow print speed of 0.1 sheet per minute.
In recent years, a drum rotation type ink-jet printer has been developed to perform color printing at a higher speed. In this ink-jet printer, a paper sheet is held on a rotary drum rotating in one direction, and a print head includes a plurality of nozzle units which are arranged along the peripheral surface of the rotary drum and eject inks of different colors onto a paper sheet rotating together with the rotary drum. Each nozzle unit includes a plurality of ink-jet nozzles disposed across the paper sheet in the axial direction of the rotary drum. The pitch of the ink-jet nozzles is set to a value equal to a desired resolution or a value two to four times greater than the resolution. The print head is positioned such that the end surfaces of the ink-jet nozzles are close to the paper sheet on the rotary drum. The print head is set to a predetermined position in the case where the pitch of the ink-jet nozzles is equal to the desired resolution. The print head is set to be movable in the axial direction of the rotary drum from the predetermined position in the case where the pitch of the ink-jet nozzles exceeds the desired resolution. When the print head is movable in the axial direction of the rotary drum, the print head is moved at a rate corresponding to the desired resolution, for each revolution of the rotary drum, and is returned to the predetermined position after the print head is moved for a distance equal to the pitch of the ink-jet nozzles. The rotation speed of the rotary drum is set to 120 rpm. In this structure, for example, a color image of A4 size can be printed out in about two or three seconds. Also, since the print head is not moved by a distance exceeding the nozzle pitch in the axial direction of the rotary drum, the number of prints to be obtained for each ink charge can be increased by placing ink cassettes of a large-capacity at a position remote from the print head and supplying inks of different colors to the respective nozzle units of the print head.
In this ink-jet printer, maintenance is carried out to prevent clogging of the nozzles and to drive out bubbles by spitting ink from the ink-jet nozzles at the non-printing time. Further, if paper particles are scattered from a paper sheet rotating together with the rotary drum at a high speed and adhere to the end surfaces of the nozzles, the paper particles soak up ink supplied to the nozzles. In the case where several thousands of sheets are printed in one day, such paper particles containing ink will likely drop on a paper sheet and arise a serious problem of degrading the print quality. Therefore, ink is also used for cleaning which removes the paper particles from the end surfaces of the ink-jet nozzles at the non-printing time or at the time when printing is interrupted.
In the ink-jet printer, therefore, ink once used maintenance as described above must be collected as waste ink. When the ink-jet printer is made compact, it is, however, difficult securely collect waste ink without smudging the neighboring components equipped in the ink-jet printer.